TIME DECAY OF THE REMANENT MAGNETIZATION IN TDAE-C-60

The time decay of the isothermal magnetization of tetrakis-dimethylaminoethylene (TDAE)-C60 after switching off a small external magnetic field has been studied between 20 and 4 K. Below Tc a remanent magnetization M0-representing the fraction of the frozen out spins-that becomes unobservably small above 12 K has been found. The relaxing magnetization fraction component M*, on the other hand, increases as Tc is approached from below. The time decay of the magnetization is rather slow below Tc and can be described by a stretched exponential form M(t)=M0+M*exp[-(t/τ)α]. The exponent α decreases from 0.14 at 4 K to 0.08 at 12 K. This shows that the spectrum of relaxation times slowly changes with temperature and becomes very wide as Tc is approached from below. No slowly relaxing component is found above Tc. The above features are characteristic of a spin-glass-like freezing process. © 1994 The American Physical Society.